This invention relates to an angular velocity sensor for detecting an angular velocity by converting deflection, caused by the Coriolis force, into an electrical signal.
A conventional angular velocity sensor of this general type is of such a construction as shown in FIGS. 6 and 7 which are a perspective view thereof and an end view thereof, respectively. More specifically, the angular velocity sensor comprises a vibratory member 1 in the form of a pillar-like metal beam of a square cross-section, piezoelectric transducers 2a to 2d affixed respectively to main surfaces 1a to 1d of the vibratory member 1, and support members 3a and 3b supporting the vibratory member 1 at respective vibration-steady points A and B of the vibratory member 1.
In the angular velocity sensor of the above construction, the vibratory member 1 is driven in a sinusoidal wave by the piezoelectric transducer 2a, affixed to the main surface 1a, to be vibrated, and in this condition, when an angular velocity is applied about a longitudinal axis Y of the vibratory member 1, the amplitude and phase increase in accordance with the applied angular velocity, and also a force (Coriolis force) sinusoidally varying at the vibration frequency of the vibratory member 1 develops in a direction perpendicular to the main surface (driving surface) 1a. As a result, vibrations are generated by this Coriolis force in the vibratory member 1 in a direction perpendicular to the driving direction at the same frequency as the driving frequency. The vibrations induced in the vibratory member 1 by this Coriolis force are detected by the piezoelectric transducer 2b affixed to the main surface 1b perpendicular to the driving surface 1a, and the magnitude of the angular velocity is detected through the amplitude and phase of the thus detected vibrations.
The piezoelectric transducers 2c and 2d affixed respectively to the main surfaces 1c and 1d are used for feedback and damping purposes, respectively.
The Coriolis force is expressed by the following formula (1): EQU F.sub.c .varies.-2m(.omega..times.V) (1)
where m represents the mass of the vibratory member 1, .omega. represents a vector of the angular velocity, and V represents a vector of the vibration speed. The vibration speed represented by the absolute value .vertline.V.vertline. of the vibration speed vector are proportional to the vibration amplitude .xi. and the vibration frequency f.sub.n as shown in the following formula (2): EQU .vertline.V.vertline..varies..xi..multidot.f.sub.n ( 2)
On the other hand, in the conventional angular velocity sensor employing the above vibratory member 1 of a square cross-section, in an ideal condition in which the vibratory member 1 is not supported by the support members, the frequency of vibration of the vibratory member 1 in a Z-direction (that is, the resonant frequency f.sub.DR on the driving side) is equal to the frequency of vibration in a X-direction (that is, the resonant frequency f.sub.RO on the detecting side). Actually, however, the support members 3a and 3b are fixed in the X-direction, and this constitutes a load on the vibrations. Therefore, the vibration frequency f.sub.DR in the X-direction is higher several tens to about one hundred Hz than the vibration frequency f.sub.OR in the Z-direction.
Further, when the vibratory member 1 is vibrated in the Z-direction, the Coriolis force appears in the X-direction as can be appreciated from the above formulas (1) and (2), and its frequency is f.sub.n, and in the vibratory member of a square cross-section, the following is established: EQU f.sub.n =f.sub.DR
However, since the resonant frequency on the detecting side is different from the resonant frequency on the driving side as described above, the following is established: EQU f.sub.n =f.sub.DR .noteq.f.sub.RO
And besides, since the difference between the frequencies f.sub.n and f.sub.RO is large, the detecting sensitivity has been poor.
This detecting sensitivity can be improved by increasing the Coriolis force F.sub.c (shown in the formula (1)) which produces the output.
However, in the angular velocity sensor of the conventional construction shown in FIGS. 6 and 7, if the width W, the height H or the length l of the vibratory member 1 is merely increased in order to increase the mass m, the vibratory member 1 can not vibrate easily, so that the vibration speed vector V becomes smaller. This necessitate a greater driving power, and there is encountered another problem that the vibratory member 1 itself is increased in size, thus increasing the size of the sensor.
In order to increase the Coriolis force by increasing the vibration speed vector V, it is considered to increase the vibration amplitude .xi. or the vibration frequency f.sub.n in connection with the above formula (2); however, the vibration amplitude and the vibration frequency f.sub.n are in opposite relation to each other, and when the vibration frequency f.sub.n is increased, the vibration amplitude is decreased. Therefore, the Coriolis force F.sub.c can not be increased by increasing the vibration speed vector V.
Accordingly, in the angular velocity sensor of the above conventional construction, it has been difficult to improve the sensitivity by increasing the Coriolis force F.sub.c.